[PATCH v6] xen: Allow a default compiled-in command line using Kconfig

[Zhongze Liu <blackskygg@gmail.com>]

Added 2 new config entries in common/Kconfig:
    CMDLINE and CMDLINE_OVERRIDE
Modifed common/kernel.c:cmdline_parse().

The 2 new entries enable an embedded command line to be compiled
in the hypervisor. CMDLINE depends on EXPERT = "y", and CMDLINE_OVERRIDE
depends on CMDLINE != "".

If CMDLINE is set, it will be parsed prior to the bootloader command line.
This order of parsing implies that if any non-cumulative options are set in
both CMDLINE and the bootloader command line, only the ones in the latter will
take effect. Further more, if CMDLINE_OVERRIDE is set to y, the whole
bootloader command line will be ignored, which will be useful to work around
broken bootloaders. A wrapper to the original common/kernel.c:cmdline_parse()
was introduced to complete this task.

This allows downstreams to set their defaults without modifying the source code
all over the place. Also probably useful for the embedded space.
(See Also: https://xenproject.atlassian.net/browse/XEN-41)

Signed-off-by: Zhongze Liu <blackskygg@gmail.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: George Dunlap <George.Dunlap@eu.citrix.com>
Cc: Ian Jackson <ian.jackson@eu.citrix.com>
Cc: Jan Beulich <jbeulich@suse.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Tim Deegan <tim@xen.org>
Cc: Wei Liu <wei.liu2@citrix.com>
---
Changed since v5:
  * remove the redundent EXPERT = "y" dependency from config CMDLINE_OVERRIDE
  * make opt_builtin_cmdline[] static and __initconst
  * changed the name do_cmdline_parse() to _cmdline_parse()
  * do a NULL check before copying cmdline to saved_cmdline
  * check the first byte of opt_builtin_cmdline to determine whether it's
    empty or not.
---
 xen/common/Kconfig  | 22 ++++++++++++++++++++++
 xen/common/kernel.c | 30 ++++++++++++++++++++++++------
 2 files changed, 46 insertions(+), 6 deletions(-)

diff --git a/xen/common/Kconfig b/xen/common/Kconfig
index f2ecbc43d6..e1c90b739a 100644
--- a/xen/common/Kconfig
+++ b/xen/common/Kconfig
@@ -237,4 +237,26 @@ config FAST_SYMBOL_LOOKUP
 	  The only user of this is Live patching.
 
 	  If unsure, say Y.
+
+config CMDLINE
+	string "Built-in hypervisor command string"
+	default ""
+	depends on EXPERT = "y"
+	---help---
+	  Enter arguments here that should be compiled into the hypervisor
+	  image and used at boot time. When the system boots, this string
+	  will be parsed prior to the bootloader command line. So if a
+	  non-cumulative option is set both in this string and in the
+	  bootloader command line, only the latter one will take effect.
+
+config CMDLINE_OVERRIDE
+	bool "Built-in command line overrides bootloader arguments"
+	default n
+	depends on CMDLINE != ""
+	---help---
+	  Set this option to 'Y' to have the hypervisor ignore the bootloader
+	  command line, and use ONLY the built-in command line.
+
+	  This is used to work around broken bootloaders. This should
+	  be set to 'N' under normal conditions.
 endmenu
diff --git a/xen/common/kernel.c b/xen/common/kernel.c
index 4b87c60845..64920e8304 100644
--- a/xen/common/kernel.c
+++ b/xen/common/kernel.c
@@ -23,6 +23,7 @@
 enum system_state system_state = SYS_STATE_early_boot;
 
 xen_commandline_t saved_cmdline;
+static const char __initconst opt_builtin_cmdline[] = CONFIG_CMDLINE;
 
 static void __init assign_integer_param(
     const struct kernel_param *param, uint64_t val)
@@ -46,18 +47,13 @@ static void __init assign_integer_param(
     }
 }
 
-void __init cmdline_parse(const char *cmdline)
+static void __init _cmdline_parse(const char *cmdline)
 {
     char opt[100], *optval, *optkey, *q;
     const char *p = cmdline;
     const struct kernel_param *param;
     int bool_assert;
 
-    if ( cmdline == NULL )
-        return;
-
-    safe_strcpy(saved_cmdline, cmdline);
-
     for ( ; ; )
     {
         /* Skip whitespace. */
@@ -147,6 +143,28 @@ void __init cmdline_parse(const char *cmdline)
     }
 }
 
+/**
+ *    cmdline_parse -- parses the xen command line.
+ * If CONFIG_CMDLINE is set, it would be parsed prior to @cmdline.
+ * But if CONFIG_CMDLINE_OVERRIDE is set to y, @cmdline will be ignored.
+ */
+void __init cmdline_parse(const char *cmdline)
+{
+    if ( opt_builtin_cmdline[0] )
+    {
+        printk("Built-in command line: %s\n", opt_builtin_cmdline);
+        _cmdline_parse(opt_builtin_cmdline);
+    }
+
+#ifndef CONFIG_CMDLINE_OVERRIDE
+    if ( cmdline == NULL )
+        return;
+
+    safe_strcpy(saved_cmdline, cmdline);
+    _cmdline_parse(cmdline);
+#endif
+}
+
 int __init parse_bool(const char *s)
 {
     if ( !strcmp("no", s) ||
-- 
2.12.0


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